In carrying out various testing and/or monitoring functions within multiple node telecommunication systems, it is necessary to identify specific internode cross-connect paths. Typically, these testing/monitoring functions are categorized as follows: new link/circuit testing; idle link monitoring; and pre-service circuit testing. New link/circuit testing is a long and involved process designed to detect transmission circuit quality. Idle link monitoring is typically performed as an ongoing maintenance function to ascertain the status of existing idle links. Pre-service circuit testing is performed immediately prior to placing a given circuit path into service (during system reconfiguration or path restoration). While the time it takes to perform such testing/monitoring may not be critical for new link testing, it is of concern in most other instances and should be kept to a minimum.
When performing the above testing and monitoring functions, a path trace identification signal ("PID") is transmitted over a specified path, and its receipt monitored at each node along that path. Within present multiple node telecommunication systems, which conform to Consultative Committee on International Telegraphy and Telephony ("CCITT") recommendation G.783, each node has the capability of storing two PID values--the received PID, and the expected PID. A two-node portion of one such system is illustrated in FIG. 1. In performing a testing or monitoring function within the illustrated system, the proper PID is transmitted by system controller 101 to each of nodes 102 and 103 via control lines 104 and 105. The PID received from system controller 101 is stored in a memory location within each node reserved for "expected" PIDs (memory location 106 for node 102, and memory location 107 for node 103). This stored "expected" PID will remain in the reserved memory within a node until the node receives a new "expected" PID from the system controller. Each node within the system acknowledges the receipt of a new "expected" PID from the system controller by transmitting a confirmation signal to the system controller.
Upon receipt of a confirmation signal from all of the nodes within the path, the system controller sends a clearance message to transmitter 108. After receiving this clearance message, transmitter 108 transmits the proper PID to nodes 102 and 103 via transmission path 109. This transmitted PID is stored in a memory location within each node reserved for "received" PIDs (memory location 110 for node 102, and memory location 111 for node 103). If all "expected" PIDs were loaded into the proper memory locations within a node prior to the reception of a "received" PID at that node, the testing or monitoring should proceed smoothly. No system alarms will be triggered as all "received" PIDs agree with all "expected" PIDs.
As stated above, in most instances the amount of time required to perform a path testing or monitoring function should be kept to a minimum. Unfortunately, in complex telecommunication systems having many nodes, a substantial amount of time may be required for a system controller to transmit "expected" PIDs to all the nodes, and for each of the nodes to acknowledge the receipt of an "expected" PID. During this period, the transmitter 108 is prohibited from transmitting a PID, since a clearance message has not been received from the system controller.
If an attempt were made to expedite the testing/monitoring function by transmitting the proper PID prior to receipt of the clearance message, a "received" PID could arrive at a node prior to the arrival of the "expected" PID sent by the system controller. This would result in a system anomaly. Since the proper "expected" PID has not arrived at the node to be loaded into the "expected" memory location within the node, it will erroneously appear that an improper PID has been received by that node (the "received" and "expected" PIDs stored in the node memory do not match). Actually, no such thing has occurred; the only real problem is a delay in signalling between the system controller and the node. Nonetheless, if this erroneous anomaly persists for more than one second, a system alarm will result (assuming the transmission system conforms to CCITT recommendation G.783). The alarm will require at least another second to be cleared, and cause the total testing/monitoring time to exceed two seconds. Such a long testing/monitoring time would be undesirable within most modern telecommunication systems.